Summary of Significant Accounting Policies (Policies)	6 Months Ended
Summary of Significant Accounting Policies (Policies)	Jun. 30, 2017
Accounting Policies [Abstract]
Adopted Accounting Pronouncements	Adopted Accounting Pronouncements Beginning in fiscal year 2017, the Company adopted Accounting Standard Update (“ASU”) No. 2016-09, Improvements to employee share-based payment accounting, which simplifies the accounting for employee share-based transactions. The amendments change, among other things, the recognition of excess tax benefits and deficiencies, the classification of those excess tax benefits on the statement of cash flows, an accounting policy election for forfeitures, the amount an employer can withhold to cover income taxes and still qualify for equity classification, and the classification of those taxes paid on the statement of cash flows. The Company adopted ASU 2016-09 in the first quarter of 2017. As a result of adopting this standard, we have made an accounting policy election to account for forfeitures as they occur. This change has been applied on a modified retrospective basis, resulting in an immaterial cumulative effect adjustment to the opening accumulated deficit on January 1, 2017. Upon adoption, the previously unrecognized excess tax benefits were recorded as a deferred tax asset, which was fully offset by a valuation allowance resulting in no impact to the accumulated deficit.
Recent Accounting Pronouncements	Recent Accounting Pronouncements From time to time, new accounting pronouncements are issued by the Financial Accounting Standards Board (“FASB”), or other standard setting bodies and adopted by the Company as of the specified effective date. Unless otherwise discussed, the impact of recently issued standards that are not yet effective will not have a material impact on the Company’s consolidated financial statements upon adoption. Under the Jumpstart Our Business Startups Act of 2012, as amended (the “JOBS Act”), the Company meets the definition of an emerging growth company, and has irrevocably elected to opt out of the extended transition period for complying with new or revised accounting standards pursuant to Section 107(b) of the JOBS Act. In May 2017, the FASB issued ASU 2017-09—Compensation—Stock Compensation (Topic 718): Scope of Modification Accounting. The amendments in this ASU provide guidance about which changes to the terms or conditions of a share-based payment award require an entity to apply modification accounting in Topic 718 to address diversity in practice. An entity should account for the effects of a modification unless all the three specified conditions are met. The current disclosure requirements in Topic 718 apply regardless of whether an entity is required to apply modification accounting under the amendments in this ASU. The amendments in this ASU are effective for all entities for annual periods, and interim periods within those annual periods, beginning after December 15, 2017, with early adoption permitted. The amendments in this ASU should be applied prospectively to an award modified on or after the adoption date. The Company has not determined the potential effects of this ASU on its consolidated financial statements. In November 2016, the FASB issued ASU No. 2016-18 (Topic 230), Restricted Cash, Statement of Cash Flows. This ASU 2016-18 requires that a statement of cash flows explain the change during the period in the total of cash, cash equivalents, and amounts generally described as restricted cash or restricted cash equivalents. Therefore, amounts generally described as restricted cash and restricted cash equivalents should be included with cash and cash equivalents when reconciling the beginning-of-period and end-of-period total amounts shown on the statement of cash flows. ASU 2016-18 is effective for public business entities for fiscal years beginning after December 15, 2017, and interim periods within those fiscal years, with early adoption permitted. The amendments in this ASU should be applied using a retrospective transition method to each period presented. The adoption of this standard is not expected to have a material impact on the Company’s consolidated financial statements. In February 2016, the FASB issued ASU No. 2016-02 (Topic 842), Leases. This ASU requires an entity to recognize assets and liabilities arising from a lease for both financing and operating leases. The ASU will also require new qualitative and quantitative disclosures to help investors and other financial statement users better understand the amount, timing, and uncertainty of cash flows arising from leases. ASU 2016-02 is effective for fiscal years beginning after December 15, 2018, with early adoption permitted. The Company has not determined the potential effects of this ASU on its consolidated financial statements. In May 2014, the FASB issued ASU No. 2014-09 (Topic 606), Revenue from Contracts with Customers, which supersedes the revenue recognition requirements in ASC 605, Revenue Recognition. This ASU is based on the principle that revenue is recognized to depict the transfer of goods or services to customers in an amount that reflects the consideration to which the entity expects to be entitled in exchange for those goods or services. The ASU also requires additional disclosure about the nature, amount, timing and uncertainty of revenue and cash flows arising from customer contracts, including significant judgments and changes in judgments and assets recognized from costs incurred to obtain or fulfill a contract. In March, April, and May 2016, the FASB issued amended guidance including clarifying guidance on principal versus agent considerations, identification of performance obligations, collectability and noncash considerations. ASU 2014-09 and its amendments are effective for public entities for annual and interim periods beginning after December 15, 2017; therefore, the Company will adopt the new revenue standards in the first quarter of 2018. Since its formation, the Company has only had transactions which are recognized in revenue which relate to its Collaboration Agreement with Sanofi S.A. The Company is evaluating whether or not the identification of performance obligations and determination of their stand-alone values would remain unchanged under the new revenue standards. The Company is still assessing the impact of the adoption of the new revenue standards on its consolidated financial statements. As the Company completes its evaluation of this new standard, new information may arise that could change the Company’s current understanding of the impact to revenue recognition. Additionally, the Company will continue to monitor industry activities and any additional guidance provided by regulators, standards setters, or the accounting profession and adjust the Company’s assessment and implementation plans accordingly.
Fair Value Measurements	Fair Value Measurements Financial assets and liabilities are recorded at fair value. The accounting guidance for fair value provides a framework for measuring fair value, clarifies the definition of fair value and expands disclosures regarding fair value measurements. Fair value is defined as the price that would be received to sell an asset or paid to transfer a liability (an exit price) in an orderly transaction between market participants at the reporting date. The accounting guidance establishes a three-tiered hierarchy, which prioritizes the inputs used in the valuation methodologies in measuring fair value as follows: Level 1—Inputs are unadjusted, quoted prices in active markets for identical assets or liabilities at the measurement date. Level 2—Inputs other than quoted market prices included in Level 1 are either directly or indirectly observable for the asset or liability through correlation with market data at the measurement date and for the duration of the instrument’s anticipated life. Level 3—Inputs reflect management’s best estimate of what market participants would use in pricing the asset or liability at the measurement date. Consideration is given to the risk inherent in the valuation technique and the risk inherent in the inputs to the model.